wanting a 3 jaw chuck

You don't really want to make a backplate out of steel. It tends to gall the spindle threads. Blank cast plates are affordable if you want to finish one yourself, but it doesn't sound like that's what you want. Just buy a 6" threaded backplate and fit it to the chuck of your choice. You wanted to know if the cheap imports are any good. That depends on your expectations. They will hold a workpiece. They'll have some run out. You have a 4 jaw so that shouldn't be a problem. The two piece jaws are definitely the way to go.
 
I am willing to try it at some point for now Id just like to get some wisdom on what 3 jaw I should be looking at, I do like that 2 piece jaw idea as using soft jaws would come in handy sometimes... setting up the 4 jaw gets old fast!
 
so from what i'm seeing it looks like id want a cast chuck ??? The forged seem to be a lot more? its an 80 yr old lathe after all how exact can it get or be...? and after I find the chuck I like i have to buy an additional backing plate to match my lathe 1 and 1 half -8 https://www.shars.com/products/work...f+Centering+Scroll+Chucks&material=cast+steel


then add this?

https://www.shars.com/ap6-b-6-1-4-x...aded-back-plate-for-cs-fs-series-lathe-chucks

anything else i'm missing? anyone own one of these brand chucks?
 
You need a plain back chuck and a cast iron backplate like the one you linked. You would probably be pleased with shars chuck. I have a small 5c 3jaw chuck that I bought from shars years ago that runs just about dead nuts. I don't use it often, but it's a handy little chuck.
 
Yes, the shars chuck is OK for what you want-most 3 jaw chucks hold within 0.005" and will repeat within 0.005", so it's good enough for most 3 jaw work.

The steel plate backing plate wouldn't be for normal use-galling is a problem if proper steel isn't selected. But it is cheap and will give proper experiance in machining a backing plate.

Off-the-shelf backing plates are not going to give the best alignment or repeatability, some especially atrocious...when you machine them to fit properly you eliminate this issue.
 
I'm curious...what would be the proper inexpensive steel to use for a backplate?
 
Personally I'd use a pre-hardened 4140 or a grade 40 cast iron. To prevent galling you'd need to make sure that the two steels have a hardness split of 5RC or so-meaning if your spindle is hardened to 30RC, you want a 25RC or a 35RC hardness for the backing plate.
 
I wouldn't use the steel regardless....but I'm thinking I could probably buy cast iron cheaper than 4140.
 
Rambin,

If you are going to go Chinese in order to save money, Shars is probably about as good as it gets. And if you go with a plain back chuck and back plate, then the chuck body material doesn't matter. Either the chuck or the back plate (or both) should come with instructions on how to fit the back plate to both your spindle and the chuck.

Before you start with the chuck, I would suggest checking the runout of your spindle register (the unthreaded area between the threads and the flange, and the flat surface of the flange that contacts the rear of the back plate). The bearings are, as you wrote, 80 years old.
 
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